/Engine/Source/Runtime/Engine/Classes/GameFramework/InputDeviceLibrary.h
Populates the OutInputDevices array with any InputDeviceID's that are mapped to the given platform user
The number of mapped devices, INDEX_NONE if the user was not found.
static int32 GetAllInputDevicesForUser ( const [FPlatformUserId](API\Runtime\Core\Misc\FPlatformUserId) UserId, [TArray](API\Runtime\Core\Containers\TArray)< [FInputDeviceId](API\Runtime\Core\Misc\FInputDeviceId) > & OutInputDevices )